An organic EL device emits light of high brightness at low voltage and, on account of this ability, it has attracted attention as a promising display device while creating an increasing demand for enhanced brightness. Of such promising materials, an ortho-metalated iridium complex, represented by tris(2-phenylpyridine)iridium complex, is attracting particular attention as it is capable of emitting light from the triplet excited state thereby producing higher quantum efficiency compared with the conventional emission of light utilizing phosphorescence. Furthermore, in recent years, developmental works focused on furnishing ortho-metalated iridium complexes with high color purity, high efficiency, and long service life required for loading into practical devices are gaining force and there is a strong demand for a process capable of producing the desired complexes in a higher yield by a simpler procedure.
The prior-art documents relating to this invention are listed below.
Patent document 1: US2004/0077862 A1
Patent document 2: WO01 /41512 A
Patent document 3: JP2003-81988 A
Patent document 4: JP2001-247859 A
Patent document 5: JP2004-168755 A
Patent document 6: JP2004-168758 A
Non-patent document 1: Inorganic Chemistry, 30, 1685 (1991)
Non-patent document 2: Journal of the American Chemical Society, 107, 1431 (1958)
Non-patent document 3: Proceeding of SPIE, 4105,119 (2001)
Non-patent document 4: Journal of the American Chemical Society, 123, 4303 (2001)
For the synthesis of ortho-metalated iridium complexes, the process described in the non-patent document 1 starts from iridium(III) acetylacetonate while the process in the non-patent document 2 starts from iridium(III) chloride. However, these processes give the complexes in low yield. The non-patent document 3 describes the extreme difficulty of synthesizing ortho-metalated complexes of iridium with homoligands from most of the ligands when the process starting from iridium(III) acetylacetonate is used.
A variety of ortho-metalated iridium complexes are synthesized from iridium(III) acetylacetonate in the patent documents 2 and 3 or from K3IrCl6 in the patent document 4. However, the yields are extremely low, ranging from 3 to 40%, in all the examples described in these documents.
The yields range from 62 to 65% in the patent document 5 wherein iridium(III) chloride is used as a staring material and the ligand is used in large excess, more than 30 times that of iridium(III) chloride in terms of equivalent, or the yield is 60% in the patent document 6 wherein a basic substance is allowed to be present in the system. However, the yields here are not sufficiently high and, besides, the use of iridium(III) chloride poses problems such as formation of difficultly separable byproducts and residual chlorine.
On the other hand, the patent document 1 gives an account of optimizing the conditions of the method described in the non-patent document 1, that is, the method which uses iridium(III) acetylacetonate as a raw material. According to this account, the ortho-metalated iridium complexes are obtained in a yield as high as 90% or more by carrying out the reaction in a polar solvent for 20 to 60 hours while setting the ratio of raw materials in a specific range and performing the acid washing as an after-treatment. However, the inventors of this invention confirmed that the ortho-metalated iridium complexes in question were difficult to obtain in such a high yield of 90% or more, although the yield improved a little over the one described in the non-patent document 1.